69 lines
3.9 KiB
ReStructuredText
69 lines
3.9 KiB
ReStructuredText
How it works
|
|
############
|
|
|
|
To understand how F4PGA works, it is best to start with an overview of the general EDA tooling ecosystem and then
|
|
proceed to see what the F4PGA project consists of.
|
|
For both ASIC- and FPGA-oriented EDA tooling, there are three major areas that the workflows need to cover: description,
|
|
frontend and backend.
|
|
|
|
.. image:: _static/images/EDA.svg
|
|
:align: center
|
|
|
|
Hardware description languages are either established (such as Verilog and `VHDL ➚ <https://IEEE-P1076.gitlab.io/>`__) or
|
|
emerging software-inspired paradigms like
|
|
`Chisel ➚ <https://chisel.eecs.berkeley.edu/>`_,
|
|
`SpinalHDL ➚ <https://spinalhdl.github.io/SpinalDoc-RTD/>`_,
|
|
`Migen ➚ <https://m-labs.hk/gateware/migen/>`_, or
|
|
:gh:`Amaranth ➚ <amaranth-lang>`.
|
|
Since early 2000s, free and open source tools allow simulating HDLs.
|
|
However, for several decades the major problem lay in the frontend and backend, where there was no established
|
|
standard vendor-neutral tooling that would cover all the necessary components for an end-to-end flow.
|
|
This pertains both to ASIC and FPGA workflows.
|
|
Although F4PGA focuses on the latter, some parts of F4PGA will also be useful in the former.
|
|
|
|
To achieve F4PGA's goal of a complete FOSS FPGA toolchain, a number of tools and projects are necessary to provide all
|
|
the needed components of an end-to-end flow.
|
|
The F4PGA toolchains consist of logic synthesis and implementation tools, as well as chip documentation projects for
|
|
chips of various vendors.
|
|
Thus, F4PGA serves as an umbrella project for several activities.
|
|
|
|
.. image:: _static/images/parts.svg
|
|
:align: center
|
|
|
|
The central resources are the so-called FPGA "architecture definitions" (i.e. documentation of how specific FPGAs work
|
|
internally) and the "interchange schema" (for logical and physical netlists).
|
|
Those definitions serve as input to frontend and backend tools, such as
|
|
`Yosys ➚ <https://yosyshq.net/yosys/>`__,
|
|
:gh:`nextpnr ➚ <YosysHQ/nextpnr>` and `Verilog to Routing ➚ <https://verilogtorouting.org/>`_.
|
|
They are created within separate collaborating projects targeting different FPGAs:
|
|
|
|
* :doc:`Project X-Ray ➚ <prjxray:index>` for Xilinx 7-Series
|
|
* `Project IceStorm ➚ <http://bygone.clairexen.net/icestorm/>`__ for Lattice iCE40
|
|
* :doc:`Project Trellis ➚ <prjtrellis:index>` for Lattice ECP5 FPGAs
|
|
|
|
More information can be found at :doc:`F4PGA Architecture Definitions ➚ <arch-defs:index>` and :doc:`FPGA Interchange ➚ <interchange:index>`.
|
|
|
|
To prepare a working bitstream for a particular FPGA chip, the toolchain goes through the following stages:
|
|
|
|
* A description of the FPGA chip is created with the information from the relevant bitstream documentation
|
|
project.
|
|
This part is done within the :gh:`F4PGA Architecture Definitions ➚ <f4pga/f4pga-arch-defs>`.
|
|
The project prepares information about the timings and resources available in the chip needed at the implementation
|
|
stage, as well as techmaps for the synthesis tools.
|
|
|
|
.. NOTE::
|
|
This stage is typically pre-built and installed as assets.
|
|
However, developers contributing to the bitstream documentation might build it.
|
|
|
|
* Then, logic synthesis is carried out in the `Yosys ➚ <https://yosyshq.net/yosys/>`__ framework, which expresses the
|
|
user-provided hardware description by means of the block and connection types available in the chosen chip.
|
|
|
|
* The next step is implementation.
|
|
Placement and routing tools put individual blocks from the synthesis description in specific chip locations and create
|
|
paths between them.
|
|
To do that, F4PGA uses either :gh:`nextpnr ➚ <YosysHQ/nextpnr>` or :gh:`Verilog to Routing ➚ <verilog-to-routing/vtr-verilog-to-routing>`.
|
|
|
|
* Finally, the design properties are translated into a set of features available in the given FPGA chip.
|
|
These features are saved in the :gh:`FASM format ➚ <chipsalliance/fasm>`, which is developed as part of F4PGA.
|
|
The FASM file is then translated to a bitstream, using the information from the bitstream documentation projects.
|